Javascript (ECMA-6) class magic method __call like PHP

Question

This is my use case

getSomeFields(persons, fields){

    let personsWithSpecificFields = [];

    _.each(persons, (person) => {

        let personSpecificFields = {};

        _.each(fields, (field) => {
            // here im thinking to modify the field to match the method name 
            // ( if something like __call as in php is available)
            // e.g. field is first_name and i want to change it to getFirstName
            personSpecificFields[field] = person[field]();

        });

        personsWithSpecificFields.push(personSpecificFields);
    });

    return personsWithSpecificFields;
}

Here is my person class

import _ from 'lodash';

export default class Person{

    // not working..
    __noSuchMethod__(funcName, args){
        alert(funcName);
    }

    constructor( data ){
        this.init(data);
    }

    init(data) {
        _.each(data, (value, key) => {
           this[key] = value;
        });
    }
}

I have gone through Monitor All JavaScript Object Properties (magic getters and setters), tried to implement this JavaScript getter for all properties but no luck.

I know i can do this by just writing another method which will transform my first_name to getFirstName and give it a shot. But is there any way to do this in ECMA-6 way like in class.

thanks.

An object instance is simply any object. Functions are objects. As such, functions can also have properties, which can also be other methods. If you want a "callable object", make it a function. — deceze, Feb 15 '17 at 08:39
Good: You searched SO for other solutions. Bad: You found one and stopped reading after the first answer. When you do ES6 anyway, try the `Proxy` solution. — Boldewyn, Feb 15 '17 at 08:45
[mdn: __NoSuchMethod__](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/noSuchMethod) is obsolete — barbsan, Feb 15 '17 at 08:46

score 43 · Accepted Answer · edited Feb 11 '19 at 18:58

You can use a proxy to detect access to a property that your object does not have, and deal with it -- this comes close to PHP's __call:

var person = new Person();
// Wrap the object in a proxy
var person = new Proxy(person, {
    get: function(person, field) {
        if (field in person) return person[field]; // normal case
        console.log("Access to non-existent property '" + field + "'");
        // Check some particular cases:
        if (field == 'first_name') return person.getFirstName;
        // ...
        // Or other cases:
        return function () {
            // This function will be executed when property is accessed as a function
        }
    }
});

You could even do this in the constructor of your class:

class Person {
    constructor(data) {
        this.init(data);
        return new Proxy(this, {
            get: function(person, field) {
                if (field in person) return person[field]; // normal case
                console.log("Access to non-existent property '" + field + "'");
                // Check some particular cases:
                if (field == 'first_name') return person.getFirstName;
                // ...
                // Or other cases:
                return function () {
                    // This function will be executed when property is accessed as a function
                    return 15; // example
                }
            }
        });
    }
    // other methods ...
    //
}

The nice thing about proxies is that the returned object is still considered an instance of the original class. With the above code, the following will be true:

new Person() instanceof Person

It works also for methods, but be careful to not call them in the proxy, but to return a function reference only. For instance, note how I did not add parentheses after `person.getFirstName` in the example code. Methods are in essence also properties, they just happen to be of the function type. — trincot, Feb 15 '17 at 10:09

score 2 · Answer 2 · answered Feb 15 '17 at 08:41

There are no special __methods() in Javascript like in PHP, so all you have are those getters, setters, toString() and valueOf().

You could give Object.defineProperty() a shot, because with that you can dynamically create getters like so:

Object.defineProperty(obj, 'first_name', {
   get: function () { return … }
});

mdn

The result is similar to:

var obj = {
  get first_name () { return … }
}

If you need to call method of an object, you can also do it like that:

var prop = 'getFirstName',
    result = obj[prop]();

What also can be done in a for loop.

also `toJSON` for `JSON.stringify` – Frondor Apr 30 '18 at 00:20 — Frondor, Apr 30 '18 at 00:20

Javascript (ECMA-6) class magic method __call like PHP

2 Answers2